LINEAR INTEGRATED CIRCUITS AND APPLICATIONS(2 marks)

LINEAR INTEGRATED CIRCUITS AND APPLICATIONS Two Mark Questions and Answers UNIT - I IC – FABRICATION 1. Mention the advantages of integrated circuits. 

Miniaturisation and hence increased equipment density. Cost reduction due to batch processing. Increased system reliability due to the elimination of soldered joints. Improved functional performance. Matched devices. Increased operating speeds. Reduction in power consumption.

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2. Write Write down the various various processes processes used to fabricat fabricatee IC’s using silicon planar

technology. 

Silicon wafer preparation. Epitaxial growth Oxidation. Photolithography. Diffusion. Ion implantation. Isolation. Metallisation. Assembly processing and packaging.

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3. What is the purpose of oxidation?

SiO2 is an extremely extremely hard protective coating and is unaffected by almost all reagents.By selective etching of SiO2, diffusion diffusion of impurities impurities through carefully defined windows can be accomplished to fabricate various components. 4. Why aluminum is preferred for metallization? 

It is a good conductor. It is easy to deposit aluminium films using vac uum deposition. It makes good mechanical bonds with silicon. It forms a low resistance contact.

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5. What are the popular IC packages available?   

Metal can package. Dual-in-line package. Ceramic flat package.

6. Define an operational amplifier.

An operational amplifier is a direct-coupled, high gain amplifier consisting of  one or more differential amplifier. By properly selecting the external components, it

can be used to perform a variety of mathematical operations. 7. Mention the characteristics of an ideal op-amp. Open loop voltage gain is infinity.   Input impedance is infinity. Output impedance is zero.  Bandwidth is infinity.  Zero offset.  +

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8. What happens when the common terminal of V and V sources is not grounded?

If the common point of the two supplies is not grounded, twice the supply voltage will get applied and it may damage the op-amp. 9. Define input offset voltage.

A small voltage applied to the input terminals to make the output voltage as zero when the two input terminals are grounded is called input offset voltage. 10. Define input offset current. State the reasons for the offset currents at the input

of the op-amp. The difference between the bias currents at the input terminals of the op-amp is called as input input offset offset current. current. The input input termin terminals als conduct conduct a small small value of dc current to bias the input transistor transistors.Sin s.Since ce the input transistors transistors cannot be made identical,there exists a difference in bias currents. 11. Define CMRR of an op-amp.

The relative sensitivity of an op-amp to a difference signal as compared to a common –mode signal is called the common –mode rejection ratio. It is expressed in decibels. CMRR= Ad/Ac 12. What are the applications of current sources?

Transistor Transistor current sources sources are widely used in analog ICs both as biasing elements and as load devices for amplifier stages. 13. Justify the reasons for using current sources in integrated circuits. 

superior superior insensitivity insensitivity of circuit circuit performance performance to power supply variations and temperature. more economical than resistors in terms of die area required to provide bias  currents of small value.  When used as load element, the high incremental resistance of current source results in high voltage gain at low supply voltages. 14. What is the advantage of widlar current source over constant current source?

Using constant current source output current of small magnitude (microamp range) is not attainable due to the limitations in chip area. Widlar current source is useful for obtaining small output currents. Sensitivity of widlar current source is less compared to constant current source.

15. Mention the advantages of Wilson current source.  

Provides high output resistance. Offers low sensitivity to transistor base currents.

16. Define sensitivity. sensitivity.

Sensitivity is defined as the percentage or fractional change in output current per percentage or fractional change in power-supply voltage. 17. What are the limitations in a temperature compensated zener-reference source?

A power supply voltage of atleast 7 to 10 V is required to place the diode in the breakdown region and that substantial substantial noise is introduced introduced in the circuit by the avalanching diode. 18. What do you mean by a band-gap referenced biasing circuit?

The biasing sources referenced referenced to VBE has a negative negative temperature temperature coefficient and VT has a positive temperature co-efficient. Band gap reference circuit is one in which the output current current is referenced referenced to a composite composite voltage that is a weighted sum of VBE and VT so that by proper weighting, weighting, zero temperature temperature coefficient can be achieved. 19. In practical op-amps, what is the effect of high frequency on its performance?

The open-loop gain of op-amp decreases at higher frequencies due to the presence presence of parasitic parasitic capacitance. capacitance. The closed-loop closed-loop gain increases increases at higher  frequencies and leads to instability. 20. What is the need for frequency compensation in practical op-amps?

Frequency Frequency compensation compensation is needed when large bandwidth bandwidth and lower closed loop gain is desired. Compensating networks are used to control the phase shift and hence to improve the stability. 21. Mention the frequency compensation methods.  

Dominant-pole compensation Pole-zero compensation.

22. What are the merits and demerits of Dominant-pole compensation?  

Noise immunity of the system is improved. Open-loop bandwidth is reduced.

23. Define slew rate.

The slew rate is defined as the maximum rate of change of output voltage caused by a step input voltage. An ideal slew rate is infinite which means that opamp’s output voltage should change instantaneously in response to input step voltage. 24. Why IC 741 is not used for high frequency applications?

IC741 has a low low slew rate rate because of the predominance of capacitance present in the circuit circuit at higher frequencies. frequencies. As frequency increases the output gets

distorted due to limited slew rate. 25. What causes slew rate?

There is a capacitor with-in or outside of an op-amp to prevent oscillation. It is this capacitor which prevents the output voltage from responding immediately to a fast changing input. 26. What is monolithic IC?

A monolithic monolithic IC is a type of "integrate "integrated d circuit" circuit" electronic electronic device that contains contains active and passive devices that are made in and on the surface of a single piece of a single crystal semiconductor, such as a Silicon (Si) wafer. A process called "planar  technology" must be used in the single block (monolith), and be interconnected to the insulating layer over the same body of the semiconductor to produce a solid integral monolithic-IC. In monolithic-ICs, the devices (transistors, diodes, resistors and capacitors) are fabricated on the same single chip of a single Silicon crystal by PLANAR technology, and have ISOLATED p-n junctions, and have interconnections adherent to the insulator layers without shorting to the adjacent areas and each other.

27. What is hybrid IC?

If the devices are interconnected by bonding wires dangling above the chip, it is a hybrid-IC. 28. What is Photolithography? Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photo mask to mask  to a light-sensitive chemical chemical "photoresist", photoresist", or simply "resist," on the substrate. A series of chemical of  chemical treatments then engraves the exposure pattern into the material underneath the photo resist. In complex integrated circuits, for example a modern CMOS, CMOS, a wafer will wafer will go through the photolithographic cycle up to 50 times. 29. What is the principle of Photolithography?

Photolithography shares some fundamental principles with photography in that the pattern in the etching resist is created by exposing it to light, light, either using a projected image or an optical mask . It is used because it affords exact control over the shape and size of the objects it creates, and because it can create patterns over an entire surface simultaneously

UNIT - II CLASSIFICATIONS OF OP-AMP 1. Mention some of the linear applications of op – amps.

Adder, subtractor, voltage –to- current converter, current –to- voltage converters,

instrumentation amplifier, analog computation ,power amplifier, etc are some of  the linear op-amp circuits. 2. Mention some of the non – linear applications of op-amps.

Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti –log amplifier, multiplier are some of the n on – linear op-amp circuits. c ircuits. 3. What are the areas of application of non-linear op- amp circuits?   

Industrial instrumentation Communication Signal processing

4. What is the need for an instrumentation amplifier?

In a number of industrial and consumer applications, the measurement of  physical quantities is usually done with the help of transducers. The output of  transducer has to be amplified So that it can drive drive the indicator indicator or display display system. This function is performed by an instrumentation amplifier. 5. List the features of instrumentation amplifier.     

high gain accuracy high CMRR  high gain stability with low temperature co-efficient low dc offset low output impedance

6. What are the applications of V-I converter?   

Low voltage dc and ac voltmeter  LED Zener diode tester 

7. What do you mean by a precision diode?

The major limitation of ordinary diode is that it cannot rectify voltages below the cut – in voltage of the diode. A circuit designed by placing a diode in the feedback loop of an op – amp is called the precision diode and it is capable of rectifying input signals of the order of o f millivolt. 8. Write down the applications of precision diode.     

Half - wave rectifier  Full - Wave rectifier  Peak – value detector  Clipper  Clamper 

9. List the applications of Log amplifiers. 

Analog computation may require functions such as lnx, log x, sin hx etc. These functions can be performed by log amplifiers

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Log amplifier can perform direct dB display on digital voltmeter and spectrum analyzer  Log amplifier can be used to compress the dynamic range of a signal  10.What are the limitations of the basic differentiator circuit? circuit? 

At high frequency, a differentiator may become unstable and break into oscillations The input impedance decreases with increase in frequency , thereby  making the circuit sensitive to high frequency noise. 11.Write down the condition for good differentiation.

For good differentiation, the time period of the input signal must be greater  than or equal to R f f C1 T > R f  C1 Where, R f f  is the feedback resistance Cf  is the input capacitance 12.What is a comparator?

A comparator is a circuit which compares a signal voltage applied at one input of  an op-amp with with a known reference reference voltage voltage at the other input. input. It is an open loop loop op amp with output + Vsat . 13.What are the applications of comparator?    

Zero crossing detector  Window detector  Time marker generator  Phase detector 

14.What is a Schmitt trigger?

Schmitt trigger is a regenerative comparator. It converts sinusoidal input into into a square wave output. The output of Schmitt Schmitt trigger swings between upper and lower  threshold voltages, which are the reference voltages of the input waveform. 15.What is a multivibrator?

Multivibrators are a group of regenerative circuits that are used extensively in timing timing applications. It is a wave shaping circuit which gives symmetric or asymmetric square output. It has two states either stable or quasi- stable depending on the type of multivibrator. 16.What do you mean by monostable multivibrator?

Monost Monostabl ablee multi multivibr vibrator ator is one which which generate generatess a single single pulse pulse of  specified duration in response to each external trigger signal. It has only o nly one stable state. Application of a trigger causes a change to to the quasi-stable quasi-stable state. An external trigger signal generated due to charging and discharging of the capacitor produces the the transition to the original stable state. 17.What is an astable multivibrator? Astable multivibrator is a free running oscillator having two quasi-stable states.

Thus, there is oscillatio oscillations ns between between these two states states and no external external signal signal are to produce the change in state.

required required

18.What is a bistable multivibrator?

Bistable multivibrator is one that maintains a given output voltage level unless an external trigger is applied . Application of an external trigger signal causes a change of state, and this output level is maintained indefinitely until an second trigger  is applied . Thus, it requires two two external triggers before it returns returns to its initial initial state. 19.Wh What at are are the requirements for producing sustained oscillatio ns in f eedback 

circuits?

For sustained oscillations, 

The total phase shift around the loop must be zero at the desired frequency of oscillation, fo. ie, AB =0 (or) 360° At fo, the magnitude of the loop gain | A β | should be equal to unity  20.Mention any two audio frequency oscillators.  

RC phase shift oscillator  Wein bridge oscillator 

21.What are the characteristics of a comparator? 

Speed of operation Accuracy Compatibility of the output

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22.What is a filter?

Filter is a frequency selective circuit that passes signal of specified band of  frequencies and attenuates the signals of frequencies outside the band 23.What are the demerits of passive filters?

Passive filters works well for high frequencies. But at audio frequencies, the inductors become problematic, as they become large, heavy and expensive.For low frequen frequency cy applic applicati ations ons,, more more number number of turns turns of wire wire must must be used used which which in turn adds to the series resistance degrading inductor’s performance ie, low Q, resulting in high power dissipation. 24.What are the advantages of active filters? 

Active filters used op- amp as the active element and resistors and capacitors as passive elements. By enclosing a capacitor in the feed back loop , inductor less active  filters can be obtained obtained 

Op-amp used in non – inverting configuration offers high input impedance and low output impedance, thus improving the load drive capacity.

25.Mention some commonly used active filters : 

Low pass filter 

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High pass filter  Band pass filter  Band reject filter.

UNIT - III APPLICATIONS OF OP-AMP 1.     

2.    

3.   

Mention some areas where PLL is widely used. Radar synchronization Satellite communication systems air borne navigational systems FM communication systems Computers. List the basic building blocks of PLL Phase detector/comparator  Low pass filter  Error amplifier  Voltage controlled oscillator  What are the three stages through which PLL operates? Free running Capture Locked/ tracking

4.

Define lock-in range of a PLL. The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lock-in range or tracking range. It is expressed as a percentage of the VCO free running frequency.

5.

Define capture range of PLL. The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range. It is expressed ex pressed as a percentage percen tage of the VCO free fre e running frequency. 6.

Define Pull-in time. The total time time taken by the PLL to establish lok is called pull-in pull-in time. It depends on the initial phase and frequency difference between the two signals as well as on the overall loop gain and loop filter characteristics. 7.

For perfect lock, what should be the phase relation between the incoming signal and VCO output signal? The VCO output output should should be 90 90 degrees degrees out out of phase with respect to the the input signal.

8. 

Give the classification of phase detector: Analog phase detector  Digital phase detector 

9.

What is a switch type phase detector?

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An electronic switch is opened and closed by signal coming from VCO and the input signal is chopped at a repetition rate determined by the VCO frequency. This type of phase detector is called a half wave detector since the phase information for only one half of the input signal is detected and averaged. 10. What are the problems associated with switch type phase detector? The output voltage Ve is proportional to the input signal amplitude. This is undesirable because it makes phase detector gain and loop gain dependent on the input signal amplitude. The output is proportional to cos making it non linear. 11.

What is a voltage controlled oscillator? Voltage controlled oscillator is a free running multivibrator operating at a set frequency called the free running frequency. This frequency can be shifted to either  side by applying a dc control voltage and the frequency deviation is proportional to the dc control voltage.

12.

On what parameters does the free running frequency of VCO depend on? External timing resistor, R T  External timing capacitor, CT  The dc control voltage Vc. 

13.

14.

Give the expression for the VCO free running frequency. f o = 0.25 / R T CT Define Voltage to Frequency conversion factor. Voltage to Frequency conversion factor is defined as, Ky = f o / Vc= 8f o /Vcc where, Vc is the the modulat modulation ion voltage voltage required required to produce produce the frequency frequency shift shift

f o

15.

What is the purpose of having a low pass filter in PLL?  It removes the high frequency components and noise. Controls the dynamic characteristics of the PLL such as capture range,  lock-in range, band-width and transient response. The charge on the filter capacitor gives a short- time memory to the PLL. 

16.

Discuss the effect of having large capture range. The PLL cannot acquire a signal outside the capture range, but once captured, it will hold on till the frequency goes goe s beyond the lock-in range. Thus , to increase the ability of lock range, large capture capture range is required. But, a large capture range will make the PLL more susceptible to noise and undesirable signal.

17.

Mention some typical applications of PLL:  Frequency multiplication/division Frequency translation  AM detection   FM demodulation  FSK demodulation.

18.

What is a compander IC? Give some examples. The term companding means compressing

and

expanding. In

a

communicatio communication n system, system, the audio signal is compressed compressed in the transmitter transmitter and expanded in the receiver. Examples : LM 2704- LM 2707 ; NE 570/571. 19.

What are the merits of companding? 

The compression process reduces the dynamic range of the signal before it is transmitted. Companding Companding preserves the signal to noise ratio of the original original signal and  avoids non linear distortion of the signal when the input amplitude is large.  It also reduces buzz, bias and low level audio tones caused by mild interference. 20.

List the applications of OTA OTA can be used in programmable gain voltage amplifier    sample and hold circuits  voltage controlled state variable filter  Current controlled relaxation oscillator.  26. List the broad classification of ADCs.  

Direct type ADC. Integrating type ADC.

27. List out the direct type ADCs. a) Flash (comparator) type converter  b) Counter type converter  c) Tracking or servo converter  d) Successive approximation type converter  28. List out some integrating type converters.  

Charge balancing ADC Dual slope ADC

29. What is integrating type converter?

An ADC converter that perform conversion in an indirect manner by first changing the analog I/P signal to a linear function of time or frequency and then to a digital code is known as integrating type A/D converter. 30. Explain in brief the principle of operation of successive Approximation ADC.

The circuit of successive approximation ADC consists of a successive approximation register (SAR), to find the required value of each bit b y trial & error. With the arrival of START command, SAR sets the MSB bit to 1. The O/P is converted into an analog signal & it is compared with I/P signal. This O/P is low or  High. This process continues until all bits are checked. 31. What are the main advantages of integrating type ADCs?  

The integrating type of ADC’s do not need a sample/Hold circuit at the input. It is possible to transmit frequency even in noisy environment or in an isolated

form. 32. Where are the successive approximation type ADC used? The Successive approximation ADCs are used in applications such as data loggers & instrumentation where conversion speed is important. 33. What is the main drawback of a dual-slop ADC? The dual slope slope ADC has long conversion time. This is the main drawback of  dual slope ADC. 34. State the advantages of dual slope ADC:

It provid provides es excell excellent ent noise noise reject rejection ion of ac signal signalss whose whose period periodss are integral multiples of the integration time T.

UNIT - IV SPECIAL ICs 1. Define conversion time.

It is defined as the total time required to convert an analog signal into its digital output. It depends on the conversion technique used & the propagation delay of circuit components. The conversion time of a successive approximation type ADC is given by T(n+1) where T---clock  period Tc---conversion time n----no. of bits 2. Define resolution of a data converter.

The resolution of a converter is the smallest change in voltage which may be produced at the output or input of the converter. n

Resolution (in volts)= VFS/2 -1=1 LSB increment . The resolution of an ADC is defined as the smallest change in analog input for a one bit change at the output. 3. Define accuracy of converter.

Absolute accuracy: It is the maximum deviation between the actual converter output & the ideal converter output. Relative accuracy: It is the maximum deviation after gain & offset errors have been removed. The accuracy of a converter is also specified in form of LSB increments or % of full scale voltage. 4. What is settling time?

It represents the time it takes for the output to settle within a specified band ±½LSB of its final value following a code change at the input (usually a full scale change). It depends upon the switching switching time of the logic circuitry circuitry due to internal parasitic capacitance & inductances. Settling time ranges from 100ns. 10µ s

depending on word length & type circuit used. 5. Explain in brief stability of a converter:

The performance of converter changes with temperature age & power supply variation . So all the relevant parameters such as offset, offset, gain, linearity error & monotonicity must be specified over the full temperature & power supply ranges to have better stability performances. 6. What is meant by linearity?

The linearity of an ADC/DAC is an important measure of its accuracy & tells us how close the converter output is to its ideal transfer characteristics. The linearity error is usually expressed as a fraction fraction of LSB increment or percentage of full-scale voltage. A good converter exhibits a linearity error of less than ±½LSB. 7. What is monotonic DAC?

A monotonic DAC is one whose analog output increases for an increase in digital input. 8. What is multiplying DAC?

A digital to analog converter which uses a varying reference voltage VR  is called a multiplying DAC(MDAC). If the reference voltage of a DAC, VR  is a sine wave give by V(t)=Vin Cos 2 f t Then, Vo(t)=VomCos(2 ft + 180º) 9. What is a sample and hold circuit? Where it is used?

A sample and hold circuit circuit is one which samples an input input signal and holds on to its last sampled value until the input is sampled again. This circuit is mainly used in digital interfacing, analog to digital systems, systems, and pulse code modulation systems. 10. Define sample period and hold period.

The time during which the voltage across the capacitor in sample and hold circuit is equal to the input voltage is called sample period. The time period during which the voltage across the capacitor is held constant is called hold period. 11. What is meant by delta modulation?

Delta modulati modulation on is a technique capable capable of performing performing analog signal signal quantization quantization with smaller smaller bandwidth bandwidth requirements. requirements. Here, the binary output representing representing the most recent sampled amplitude amplitude will be determined on the basis of  previous sampled amplitude levels. 12. Draw the Pin digram of IC 555.

13. Mention some applications of 555 timer:      

Oscillator  pulse generator  ramp and square wave generator  mono-shot multivibrator  burglar alarm Traffic light control.

14. List the applications of 555 timer in monostable mode of operation:    

Missing pulse detector  Linear ramp generator  Frequency divider  Pulse width modulation.

15. List the applications of 555 timer in Astable mode of operation:  

FSK generator  Pulse-position modulator 

16. List the applications of 555 timer in monostable mode of operation: 

Missing pulse detector 

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Linear ramp generator  Frequency divider  Pulse width modulation.

17. List the applications of 555 timer in Astable mode of operation:  

FSK generator  Pulse-position modulator 

18. What is a voltage regulator?

A voltage regulator is an electronic circuit that provides a stable dc voltage independent of the load current, temperature, and ac line voltage variations. 19. Give the classification of voltage regulators: Series / Linear regulators   Switching regulators. regulators.

UNIT – V APPLICATION ICs 1. What is opto coupler coupler an opto-isolat opto-isolator, or, also called called an optocoupler, optocoupler, photocoupler, photocoupler, or optical optical isolator, isolator, is "an electronic device designed to transfer electrical signals by utilizing light waves to provide coupling with electrical isolation between its input and output".[1] The main purpose of an opto-isolator is "to prevent high voltages or rapidly changing voltages on one side of the circuit from damaging components or distorting transmissions on the other side 2.

What is a linear voltage regulator?

Series or linear regulator uses a power transistor connected in series between the unregulated dc input and the load and it conducts in the linear region .The output voltage is controlled by the continuous voltage drop taking place across the series pass transistor. 3.

What is a switching regulator?

Switching regulators are those which operate the power transistor as a high frequency on/off switch, so that the power transistor does not conduct current continuously. This gives improved efficiency over series regulators. 4.

What are the advantages of IC voltage regulators? Low cost  High reliability   Reduction in size Excellent performance 

5.

Give some examples of monolithic IC voltage regulators: 78XX series fixed output, positive voltage regulators 



79XX series fixed output, negative voltage regulators 723 general purpose regulator.

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6.

What is the purpose of having input and output capacitors in three terminal IC regulators? A capacito capacitorr connected connected between the input input termi terminal nal and and ground ground cancels cancels the inductive inductive effects effects due to long distribut distribution ion leads. The output capacitor improves the transient response.

7.

Define line regulation. Line regulation is defined as the percentage change in the output voltage for a change in the input voltage. It is expressed in milli volts or as a percentage of the output voltage.

8.

Define load regulation. Load regulation is defined as the change in output voltage for a change in load current. It is expressed in millivolts millivolts or as a percentage of the output voltage.

9.

What is meant by current limiting? Current limiting refers to the ability of a regulator to prevent the load current from increasing above a preset value.

10. Give the drawbacks of linear regulators: 

The input step down transformer is bulky and expensive because of low line frequency. Because of low line frequency, large values of filter capacitors are required  to decrease the ripple. Efficiency Efficiency is reduced due to the continuous continuous power dissipation dissipation by the  transistor as it operates in the linear region. regulators? 11. What is the advantage of switching regulators? 

Greater efficiency is achieved as the power transistor is made to operate as low impedance switch. Power transmitted across the transistor is in discrete pulses rather  than as a steady current flow.

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By using suitable switching switching loss reduction reduction technique, technique, the switching switching frequency can be increased so as to reduce the size and weight of the inductors and capacitors.

12. What is an opto-coupler IC? Give examples.

Opto-coupler IC is a combined package of a photo-emitting device and a photo- sensing device. Examples for opto-coupler circuit: LED and a photo diode, LED and photo transistor, LED and Darlington. Examples for opto-coupler IC: MCT 2F , MCT 2E . 13. Mention the advantages of opto-couplers:

     

Better isolation between the two stages. Impedance problem between the stages is eliminated. Wide frequency response. Easily interfaced with digital circuit. Compact and light weight. Problems such as noise, transients, contact bounce, are eliminated.

14. What is an isolation amplifier?

An isolation amplifier is an amplifier that offers electrical isolation between its input and output terminals 15. What is the need for a tuned amplifier?

In radio or TV receivers, it is necessary to select a particular channel among all other available channels. Hence some sort of frequency selective circuit is needed that will allow us to amplify the frequency band required and reject all the other  unwanted signals and this function is provided by a tuned amplifier. . 16. Give the classification of tuned amplifier: (i) Small signal tuned amplifier   Single tuned Double tuned  Stagger tuned  (ii) Large signal tuned amplifier.